pstore: Fix flags to enable dumps on powerpc

commit 041939c1ec54208b42f5cd819209173d52a29d34 upstream.

After commit c950fd6f kernel registers pstore write based on flag set.
Pstore write for powerpc is broken as flags(PSTORE_FLAGS_DMESG) is not set for
powerpc architecture. On panic, kernel doesn't write message to
/fs/pstore/dmesg*(Entry doesn't gets created at all).

This patch enables pstore write for powerpc architecture by setting
PSTORE_FLAGS_DMESG flag.

Fixes: c950fd6f ("pstore: Split pstore fragile flags")
Signed-off-by: Ankit Kumar <ankit@linux.vnet.ibm.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>